1,721,032 research outputs found
New constraints on the formation of heterogeneous oceanic crust at slow spreading ridges: a detailed petro-geochemical study of the olivine-rich troctolites from Atlantis Massif (MAR, IODP Hole U1309D, 30°N)
No full textFossil oceanic core complexes recognized in the blueschist metaophiolites of Western Alps and Corsica
No full textTethyan ophiolites show an apparent poorly organized association of ultramafic and mafic rocks. By contrast to the complete mantle-crustal sections of Semail-type ophiolite sheets, Tethyan ophiolites are characterized by a smaller amount of mafic rocks (gabbros and basalts), by the absence of any sheeted dyke complex and by the frequent occurrence of oceanic sediments stratigraphically overlying mantle-derived peridotites and associated gabbroic intrusions. Therefore, they are considered as typical remnants of oceanic lithosphere formed in slow- spreading environment or in ocean–continent transition at distal passive margins. In the very first models of formation of the Tethyan ophiolites, in the years 1980, the geodynamical processes leading to mantle unroofing were poorly understood due to the paucity of data and concepts available at that time from the present-day oceans. In particular, at that time, little work had focused on the distribution, origin and significance of mafic rocks with respect to the dominant surrounding ultramafics. Here, we reconsider the geology of some typical metaophiolites from the Western Alps and Corsica, and we show how results from the past decade obtained in the current oceans ask for reassessing the significance of the Tethyan ophiolites in general. Revisited examples include a set of representative metaophiolites from the blueschists units of the Western Alps (Queyras region) and from Alpine Corsica (Golo Valley). Field relationships between the ophiolitic basement and the metasedimentary/metavolcanic oceanic cover are described, outlining a typical character of the Tethyan ophiolite lithological associations. Jurassic marbles and polymictic ophiolite metabreccias are unconformably overlying the mantle-gabbo basement, in a way strictly similar to what is observed in the non-metamorphic Appennine ophiolites or Chenaillet massif. This confirms that very early tectonic juxtaposition of ultramafic and mafic rocks occurred in the oceanic domain before subduction. This juxtaposition resulted from tectonic activity that is now assigned to the development of detachment faults and to the formation of Oceanic Core Complexes (OCCs) at the axis of slow spreading ridges. This fundamental Plate Tectonics process is responsible for the exhu- mation and for the axial denudation of mantle rocks and gabbros at diverging plate boundaries. In addition, field relationships between the discontinuous basaltic formations and the ultramafic–mafic basement indicate that this tectonic stage is followed or not by a volcanic stage. We discuss this issue in the light of available field constraints
Melt-rock reaction at the oceanic peridotite-gabbro transition through combined EBSD and in-situ mineral geochemistry on the Erro-Tobbio peridotitic body (Liguria, Italy)
No full textMelt/rock reaction at the oceanic mantle-crust transition, through combined EBSD and in-situ mineral geochemistry studies on the Erro-Tobbio peridotites (Ligurian ophiolites, Italy)
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Multi-stage melt-rock interactions in the Monte Maggiore peridotitic body: textural, structural, and chemical evolution from peridotite to hybrid troctolite
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Textural evolution of a dunitic matrix during formation of hybrid troctolites: insights from the Monte Maggiore peridotitic body (Corsica, France)
No full textChemical profiles along olivine crystallographic axes: a record of the melt-rock interaction sequence forming Hole U1309D Olivine-rich troctolites (Atlantis Massif, MAR, 30°N)
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